Carbon black with large primary particle size as reheat additive for polyester and polypropylene resins

ABSTRACT

Reheat characteristics of polyethylene and polypropylene resins, including reheating time and resin color, are improved by adding to the resin carbon black with a primary particle size in the range of 200 to 500 nm as an infrared absorber. Thermal carbon blacks having this primary particle size are preferred over Furnace carbon blacks. Injection stretch-blow molded bottles and other thermoformed products are made from resins with carbon black infrared absorber.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is divisional application of U.S. patentapplication Ser. No. 12/879,045 to Harrison et al., filed Sep. 10, 2010,issued as U.S. Pat. No. 8,097,671, which is a divisional application ofU.S. patent application Ser. No. 10/984,506, filed Nov. 8, 2004, issuedas U.S. Pat. No. 7,816,436, each of which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention relates to the manufacture of bottles, containersand other articles from polyester and polypropylene compositions thatexhibit faster heat-up rates as a result of the addition of low levelsof carbon black to the polymer. Faster heat-up rates reduce the time andenergy needed to manufacture containers made from polyethyleneterephthalate and polypropylene by injection stretch blow molding.

BACKGROUND OF THE INVENTION

Polymer compositions, such as polyethylene terephthalate (PET) andpolypropylene (PP) are well known packaging materials. For example, U.S.Pat. No. 4,340,721 describes a PET composition used to manufacturebeverage bottles and other containers (hereinafter referred to as“bottles”) by various molding methods.

Bottles made from PET, such as for mineral water and carbonatedbeverages, are generally made by injection stretch-blow molding. Thistechnique involves the injection molding of a “preform” which issubsequently blow molded into the final bottle shape. This may becarried out on separate injection mold and stretch-blow machines or on asingle machine where the two steps are combined. Preforms usuallyconsist of a threaded neck with a shortened bottle body shape 8 to 20 cmlong with a material thickness between 3 mm and 6 mm. In order to blowthe bottle, the preform is reheated by infrared lamps to a specifictemperature above the glass transition point of the PET, such that itcan be stretched and blown into a mold of the desired shape.

In general, PET resins have a poor ability to absorb infrared radiation.The preform heating and stretch blow moulding stage therefore becomes arate-limiting factor in the overall bottle production process.Furthermore, the preform heating step also requires a significant amountof energy. To address this, many grades of commercial PET bottle resinincorporate additives to improve the heat-up rate (hereinafter referredto as “faster reheat”) of the preforms. The aim is to increase the rateof blowing, and thereby the overall productivity, as well as to reducethe energy required to reheat the preform.

In practise, the additives used to improve reheat in PET are finelydispersed inert black materials that strongly absorb radiant energy atthe wavelengths emitted by the infrared lamps (generally between 500 and2000 nm) used in stretch blow moulding machines. Examples of thematerials used in PET are carbon black, as described in U.S. Pat. No.4,408,004, graphite as described in U.S. Pat. Nos. 5,925,710 and6,034,167, black iron oxides as described in U.S. Pat. No. 6,022,920,iron phosphide and iron silicide as described in U.S. patent applicationpublication 2003/0018115 A1 and black spinel pigments as described inU.S. patent application publication 2002/0011694 and U.S. Pat. No.6,503,586. The addition levels of these additives, in order to obtainthe desired level of reheat improvement, is generally between 5 and 100ppm.

Improved reheat in PET has also been shown by the use of antimony metalparticles. These particles are usually deposited by a chemical reactionbetween the antimony polymerisation catalyst and a reducing agent (forexample phosphorous acid) during the melt polymerisation stage, asdescribed in U.S. Pat. Nos. 5,419,936 and 5,529,744.

Whilst the reheat improvement described above generally applies to PET,a further consideration, and a main embodiment of this invention, is theimprovement of reheat in PP resins. PP is increasingly replacing PET forbottles for many beverage applications due to its lower material cost.U.S. Pat. No. 6,258,313 teaches that injection stretch blow molding of aPP preform is possible if the preform is heated simultaneously both fromthe outside and inside. Nevertheless, until recently it has been moredifficult to produce satisfactory beverage bottles from PP than PET bythis method. Firstly, polypropylene has a lower density and specificheat than PET and hence exhibits a significantly narrower processingwindow. Secondly, polypropylene suffers from the same limitations as PETin terms of its poor ability to absorb IR radiation. In general,polypropylene also has a greater opacity than PET, which detracts fromits aesthetic appearance. The industry therefore continues to seek waysto improve the IR absorption properties of polypropylene such that itcan be used to make beverage bottles on the same injection stretchblow-molding equipment as PET.

For PET and PP resin manufacturers who do not wish or are unable to useother black body absorbers, a convenient additive for improved reheat iscarbon black. Carbon black offers the advantages of inertness, low cost,and ease of dispersion in the resin compared to other absorbingmaterials. Carbon black also exhibits a high degree of absorption atnear-infrared wavelengths. It also has a high emissivity and hence ahigh proportion of the increase in temperature of the particlesresulting from this absorption is transferred to the surroundingpolymer. Thus very low levels of carbon black need to be added to thepolymer in comparison to other black materials.

In using these additives, bottle manufacturers aim to maximise theimprovement in reheat whilst minimising the impact on the colour andhaze of the final bottle. By definition, the addition of a blackmaterial to the resin leads to darker bottles that are perceived to beless attractive than perfectly colourless ones. A particulardisadvantage of carbon black is the dark hue and yellow-brown color toneimparted to the resin containing even very small amounts of carbonblack. This problem becomes increasingly apparent as manufacturers aimfor progressively faster reheat rates. Black materials that meet adesired combination of reheat and color performance continue to besought.

SUMMARY OF THE INVENTION

This invention is a method for improving the reheat characteristics ofPET and PP preforms by the addition of carbon black with a primaryparticle size in the range 200 to 500 nm as an infrared absorber in theresin. This form of carbon black allows faster preform heat-up rates inPET and PP preforms at any specific level of enhanced reheat.Furthermore, the addition of carbon black with this particle sizeunexpectedly yields superior resin color to that obtained by using theother types of carbon black described in the prior art.

Particularly preferred carbon blacks have a primary particle size in therange of 200 to 500 nm and are formed by the carbon black ThermalProcess.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in the following detaileddescription with reference to the following drawings, wherein:

FIG. 1 is a schematic representation of the plaque test for measuringreheat in PET and PP used to obtain the data in Examples 1 and 2;

FIG. 2 is a graph of the plaque reheat versus L* color component of theplaque for the carbon black containing PET compositions described inExample 1;

FIG. 3 is a graph of the plaque reheat versus a* color component of theplaque for the carbon black containing PET compositions described inExample 1;

FIG. 4 is a graph of the plaque reheat versus b* color component of theplaque for the carbon black containing PET compositions described inExample 1;

FIG. 5 is a graph of the plaque reheat versus L* color component of theplaque for the carbon black containing PP compositions described inExample 2;

FIG. 6 is a graph of the plaque reheat versus a* color component of theplaque for the carbon black containing PP compositions described inExample 2;

FIG. 7 is a graph of the plaque reheat versus b* color component of theplaque for the carbon black containing PP compositions described inExample 1; and

FIG. 8 is a graph of plaque L* versus cycle time savings for PPcompositions containing a Furnace and Thermal carbon black reheat agentin a PP bottle blowing process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The use of carbon black to improve reheat was first described in U.S.Pat. No. 4,408,400 to Pengilly, and subsequently in U.S. Pat. Nos.4,476,272 and 4,535,118 also to Pengilly. These patents contain specificclaims for the addition of 1 to 5.5 ppm carbon black with a particlesize of 10 to 100 nm, but with a preferred particle size range of 15 to30 nm. The specific types of carbon black described in the examples areforms referred to as “Channel” or “Furnace” black, with a particle sizeof 25 nm. There are no examples in the Pengilly patents of any type ofcarbon black other than Channel and Furnace blacks. Furthermore, thePengilly patents do not state that particle size has any influence onthe color of the resin relative to the degree of reheat improvement.

We have now shown that the optical and infrared absorptioncharacteristics resulting from the presence of these black additives atlow concentrations is highly dependent on this particle size.Specifically, we have shown that 200 to 500 nm particles unexpectedlyproduce a superior resin color as compared to 10 to 100 nm carbon blackparticles at any level of improved reheat. With 200 to 500 nm particlesthe colour of the resin, and hence the final bottle or other productformed from the resin, is lighter in appearance and grey-blue in colortone. In contrast, with 10 to 100 nm carbon black particles the resin isyellow-brown in color tone and substantially darker at any equivalentlevel of reheat.

It is well understood that for that for clear beverage bottles, alighter and grey-blue appearance is commercially preferable to a darkerand yellow-brown appearance. Thus as defined by, for example the 1976CIE designation of color and brightness, the preferred characteristicsin a clear bottle are an L* as high as possible, an a* as close aspossible to zero and a b* as close as possible to zero. In this case L*is a measure of brightness and can range from 0 (absolute black) to 100(absolute white). a* is a measure of the red-green color component wherean increasingly negative value signifies increasing green color tone andan increasingly positive value signifies increasing red color tone. b*is a measure of the yellow-blue color component where an increasinglynegative value signifies increasing blue color tone and an increasinglypositive value signifies increasing yellow color tone. Whilst a b* nearto zero is preferable, a negative b*, or blue color tone, is preferableto bottle manufacturers than a positive b*, or yellow color tone.“Yellowness” may generally be perceived as degradation or impurity inthe resin, whereas “blueness” is not. The main finding of this inventionis that the addition of carbon black with a particle size above 200 nm,preferably above 250 nm, leads to higher resin L*, lower resin b* andsimilar resin a* in comparison to carbon blacks with a particle size of10-100 nm. Hence, this form of carbon black demonstrates superior colorin the final bottle produced by injection stretch blow moulding or otherproducts produced from the resin.

As the concentration of a reheat additive is increased, the resingenerally becomes progressively darker and less acceptable for themanufacture of clear and colorless bottles. The level of reheat that canbe achieved by the addition of carbon black is therefore limited by themanufacturers' color specification for the final bottle. The reheat thatcan be obtained by the use of carbon blacks with primary particle sizesof 200 to 500 nm, preferably 250 to 300 nm, is substantially faster atany acceptable limit of resin color, and hence more desirable to bottlemanufacturers, than by the use of carbon blacks with particle sizes of10 to 100 nm.

To produce clear bottles, the carbon black particle size preferablyshould not exceed 500 nm in diameter, and is preferably between 200 and500 nm, and most preferably between 250 and 300 nm. The amount of carbonblack employed may range from 3 ppm to 50 ppm based upon the weight ofthe resin. The level used is determined by the level of reheatimprovement that is required by the manufacturer. If necessary, masterbatches of the PET or PP containing quantities of the carbon black inhigher concentrations can be made for subsequent blending with thepolymer to obtain the desired levels of carbon black in the finalbottle.

Suitable PET and PP or compositions in the present invention may be anyresin from which bottles, other containers or thermoformed articles inwhich an improvement in reheat is required, can be made. The method ofmanufacturing the PET or the PP may be any conventional process thatpermits the addition of the carbon black to the resin. The carbon blackmay be introduced to the polymer at any stage in the manufacturingprocess. The carbon black is inert and does not interact with any otheradditives, decompose, transform or affect the resin during themanufacturing process and therefore imposes no limitations on themethods of manufacture that may be used.

PET Compositions and Test Samples from these Compositions

In order to demonstrate the present invention for the reheat of PETresin, samples were made in a 70 Kg scale in a batch autoclave reactor.To isolate the effect of the reheat additive all of the batches weremade to a fixed composition, with the exception of the type andconcentration of added carbon black. The composition used is wellunderstood to be a typical formulation from which PET beverage bottlescan be manufactured.

The resin was produced by a conventional process of directesterification of terephthalic acid with monoethylene glycol, to producea “monomer” to which catalyst, stabiliser, color toners and the carbonblack were added. The monomer was then polymerised under vacuum to atarget melt viscosity of 0.60 dl/g, at which point the resulting meltwas cast from the autoclave, quenched and cut into granules to give anamorphous “base” resin. 25 Kg batches of the base resin were finallycrystallised and further polymerised in the solid state at 210 C in afluid-bed reactor to a target melt viscosity of 0.82 dl/g to obtain therequired polymer viscosity at which bottles could be blown.

To compare the relationship between resin color and reheat, thesolid-state polymerised resins containing different types and levels ofcarbon black were molded into 10 cm diameter×4 mm thick circular plaqueson an injection moulding machine. The color and reheat of the resin wasmeasured on these plaques as described below to produce the data shownin Example 1.

PP Compositions and Test Samples from these Compositions

To demonstrate the present invention for the reheat of PP, compositionscontaining different types of carbon black were prepared by compoundingcarbon blacks into a control sample of PP resin using two extruders inseries. The base PP used for these experiments is a typical grade of PPfrom which clear bottles can be produced.

The carbon black was first added to the PP granules and the blendcompounded through a twin-screw extruder to produce an initialdispersion of the carbon black in the resin. This material was then fedthrough a single screw extruder fitted with a Cavity Transfer mixer toproduce the final composition. A Cavity Transfer mixer was specificallyused to create the optimum dispersion of particulate additives and hencethe best possible dispersion of the carbon black in the PP.

The final PP compositions were used to injection mould plaques in thesame way and on the same machine as for the PET compositions. The colorand reheat of the plaques were measured as described below, and gave thedata shown in Example 2. The preform blowing data shown in Example 3 wasalso obtained from compositions made in this way.

PET and PP Reheat Test Methods

The present invention is based on the relationship between the color ofthe resin and the particle size of the carbon black used to achieve thedesired level of reheat. The PET reheat measurements described hereinare a based on an arbitrary, but clearly defined, scale of values fromthe INVISTA standard preform reheat test (INVISTA Standard Test Methodfor Minimum Blowing Time Test No. MST 116). This test compares theminimum blowing time required to produce a clear PET bottle. The minimumblowing time required for a preform made from the test polymer iscompared with that for a preform made from a “zero seconds reheat”standard polymer. The difference is quoted as the “reheat” of the testsample. Thus, faster reheat, which requires a shorter overall blowingtime as result of the faster rise in temperature of the preform, isrepresented by a negative number, this being the number of seconds lessthan the overall blowing time for the zero seconds reheat preform.Similarly, slower reheat is represented by a positive number, this beingthe number of seconds more overall blowing time required for the testsample preform than for the zero seconds reheat standard preform.

The minimum blowing time is defined as the point at which a clear andcrystallisation-free bottle can be obtained. The overall blowing time isthe total of the heating time required to raise the preform to atemperature at which a crystallisation-free bottle can be blown, plusthe time to blow and stretch the preform itself. The preform-heatingcomponent of the overall blowing time is influenced only by the infraredabsorptive characteristics of the resin. However, the preform stretchingand blowing time component can be influenced to some extent by theactual composition of the resin (for example comonomer content) and itsviscosity.

Thus, in order to eliminate differences in composition and viscositybetween test samples and the standard, a secondary test was used basedon the temperature rise of injection moulded plaques. In this test, asillustrated in FIG. 1, test samples and standard samples of knownpreform reheat are moulded into 10 cm diameter×4 mm thickness circularplaques 10. These plaques 10 are heated for a fixed time of 90 secondsbeneath a Phillips 175 W infrared lamp 12. After 90 seconds thetemperature of the plaque 10 is measured using a Minolta Cyclops 300AFinfrared pyrometer 14 focused on the upper surface of the plaque 10. Thelamp 12 is fitted with a shutter 16 that opens to expose the plaque 10to the lamp 12 for 90 seconds, and then closes. The pyrometer 14automatically measures the temperature of the plaque 10 at the point atwhich the shutter 16 closes. The plaque 10 is supported on turntable 18that is rotatable by motor 20. The plaque is rotated beneath the lamp 12to ensure an even temperature distribution. The infrared lamp 12,pyrometer 14 and plaque turntable 18 are all fixed to the same framework(not shown) to prevent relative movement between the components whilstthe temperature data is being obtained. The test is carried out in afixed temperature environment, and on plaques that have been stored inthis environment, to remove any possible influence of the startingtemperature or the environment on the final plaque temperature.

Reheat values are obtained by measuring the temperature rise of plaquesmade from at least three different “standard” polymers of known preformreheat, in the range zero to minus 12 seconds. For the data obtained inthe present invention the reheat of the standard plaques was zero, minus6 and minus 10 seconds. These standard plaques had the same compositionand viscosity as the zero second standard plaques. The preform reheatversus the plaque temperature of these is plotted to give a“calibration” line. In our experience of this test, the relationshipbetween plaque temperature rise and the preform reheat for samples withthe same viscosity and composition over a range of reheat values isalways linear. Thus, by measuring the plaque temperature of testplaques, the equivalent preform reheat can be simply read-off from thelinear calibration line produced from standard plaques measured at thesame time. The PET reheat values quoted herein are based on the plaquetest. Since all the samples produced were made to the same polymerformulation and viscosity, the reheat values would be the same ifmeasured by the preform test.

By the INVISTA preform and plaque tests, the reheat of most grades ofPET from which beverage bottles are manufactured falls between minus 15(−15) and plus 5 (+5) seconds.

For PP, the same test was used except that, in the absence of anexisting PP preform reheat standard by which the test could becalibrated, only the final plaque temperature itself was used as shownin Example 2.

In the PP blowing experiment data shown in Example 3, the reheat ofcompositions made with the different types of carbon black is alsocompared in terms of the cycle time reduction observed during theexperiment.

PET and PP Color Test Method

The color measurements described in the present invention were madeusing a Gardner BYK Color-View spectrophotometer Model No. 9000. Thesame procedure was used for plaques molded from both the PET and PPcompositions. Color was measured by placing each plaque beneath astandard white tile and recording the reflected color of the tile usingthe 1976 CIE L*, a* and b* designation of color and brightness. Thebacking tile had the color values L*93.10, a*0.13 and b*3.55.

The plaque color is a useful indication of the preform color, being ofcomparable wall thickness, but simpler to measure by conventionalmeasurement techniques. Color measurements were also made on the polymergranules. In the case of PET, measurements were made on granules in theamorphous state before being solid-state polymerised, and on granules inthe crystalline state after solid-state polymerisation. Whilst theseshowed the same relationships between reheat and color as plaques,plaque values were taken as the truest reflection of the color of thepreform and final bottle.

Carbon Blacks

Around 95% of global production of carbon black is based on the Furnaceand the Channel processes (hereinafter referred to collectively as“Furnace carbon blacks”). Carbon blacks made by these processes have aprimary particle diameter in the range 10 to 100 nm depending on theindividual process. In contrast, a more recent and less widespreadproduction method known as the Thermal process, produces a largerprimary particle with a diameter in the range 200 to 500 nm (hereinafterreferred to as “Thermal carbon blacks”). The difference in primaryparticle size between these two forms of carbon black is a consequenceof the different conditions in the respective manufacturing processes.Preferably, the 200-500 nm particle size carbon blacks used as reheatadditives in the present invention were made by the Thermal process.

The “primary particles” referred to above are the smallest, irreducibleparticles of material that constitute the carbon black. It is wellunderstood that different forms of carbon black exhibit varying degreesof aggregation of these primary particles on the sub micron and micronscale. The degree of this aggregation is known to have a significantinfluence on its physical properties. However, we have shown that thishas little influence on the optical and absorptive properties of carbonblack when finely dispersed at very low concentrations in PET or PP, andhence only the primary particle size is relevant to its application forimproved reheat.

EXAMPLE 1 Polyethylene Terephthalate

Base polymer PET samples to demonstrate the present invention were madeon a 70 Kg scale batch reactor. This consists of two separate stirredvessels, the first for the direct esterification of terephthalic acidwith ethylene glycol under high pressure to produce the “monomer” andthe second for the polymerisation of the monomer under vacuum(hereinafter referred to as the “autoclave”). With the exception of thecarbon black reheat additive, all the samples in this example were madewith identical formulations and under identical process conditions.

59.3 Kg of terephthalic acid, 1.2 Kg isophthalic acid and 29.0 Kg ofethylene glycol were charged to the esterification vessel and reacted at250 C and at 40 pounds per square inch above atmospheric pressure until9 liters of water had been removed from the reaction mixture. The vesselwas then restored to atmospheric pressure and 10.5 g of phosphoric acidadded and stirred into the monomer to act as the polymer stabiliser. Thecontents of the esterification vessel were then pumped to the autoclavewhere 19.25 g antimony trioxide (the polymerisation catalyst) was addedin the form of a solution in ethylene glycol and stirred into themixture. 0.14 g Clariant Blue-RBL dye and 0.07 g Clariant Red-GFPpigment were then added as the polymer color toners and stirred into themixture. Finally the carbon black reheat additive, to give the desiredconcentration in the polymer, was added and stirred into the mixture.After all the additives had been charged, the autoclave pressure wasslowly reduced to the best possible vacuum and the temperature raised to290 C in order to carry out polycondensation of the monomer. Thepolymerisation reaction was terminated at a target melt viscosity of0.60 dl/g as determined by the torque loading indication on theautoclave agitator. At this point, the molten polymer was extruded,quenched in a cold water bath and cut into granules.

In all cases the carbon black slurries were prepared in the form of 1%w/w slurries in ethylene glycol which were stirred on a Silverson highshear mixer for a period of at least two hours before being charged tothe autoclave. The correct amount of slurry was immediately weighed outand charged to the autoclave after stirring to prevent any possibilityof settling or agglomeration.

25 Kg batches of the amorphous base resin were re-polymerised in thesolid-state at a temperature of 210 C in a fluid-bed reactor where theflow of nitrogen was sufficient to fluidise the polymer granules. Theprocess was terminated when the polymer had reached a target meltviscosity of 0.82 dl/g, as indicated by polymer samples taken from thereactor and measured on a Davenport Melt Viscometer at 295C.

5 Kg samples of the 0.82 dl/g solid state polymerised resin were driedfor 4 hours at 175 C and then molded into 4 mm thick×10 cm diameter wideclear plaques on a Krupps KR35 single screw-injection moulding machine.These plaques were clean and free of surface contaminants, and had flatupper and lower surfaces. Reheat and color measurements were made onthese plaques using the methods described above.

All of the PET plaque reheat and color data for the samples made for thepresent invention are shown in Table 1. In Table 1, the carbon blacksare grouped according to manufacturing process (Furnace or Thermal) andthe primary particle diameter claimed by the manufacturer.

TABLE 1 PET plaque reheat and color data (Example 1) Mean particlePlaque Addition diameter/nm reheat/s Plaque Plaque Plaque Carbon blackManufacturer Type level/ppm (manufacturer) (mean 4 tests) L* a* b* None— — — 0.2 83.1 −1.1 4.1 None — — — 1.0 80.9 −0.7 4.8 Printex F alphaDegussa Furnace 1 20 −1.0 80.2 −1.1 5.2 Printex F alpha Degussa Furnace2 20 −4.2 76.4 −1.0 6.0 Printex F alpha Degussa Furnace 3 20 −6.1 72.9−0.5 5.2 Printex F alpha Degussa Furnace 5 20 −9.0 67.0 −0.3 6.7 PrintexF alpha Degussa Furnace 5 20 −9.8 64.0 −0.1 8.7 Vulcan 6 Cabot Furnace 124 −2.6 78.1 −1.5 6.2 Vulcan 6 Cabot Furnace 2 24 −1.7 76.6 −0.9 6.6Vulcan 6 Cabot Furnace 5 24 −10.4 63.5 −0.3 7.8 Special Black 4 DegussaFurnace 2 25 −0.7 77.6 0.4 4.2 Special Black 4 Degussa Furnace 3 25 −3.574.8 0.6 4.8 Special Black 4 Degussa Furnace 5 25 −7.5 67.3 0.4 6.7Elftex 254 Cabot Furnace 2 25 −1.6 77.6 −1.4 7.8 Elftex 254 CabotFurnace 5 25 −9.4 66.1 −0.4 7.5 Raven 860 Columbian Furnace 5 40 −2.871.6 0.0 8.9 Monarch 120 Cabot Furnace 5 75 −8.5 68.8 −0.6 6.6 Raven 22DColumbian Furnace 5 83 −7.6 68.7 0.1 6.2 Raven 410 Columbian Furnace 5100 −7.1 71.8 −0.8 6.8 Carbocolor Cancarb Thermal 5 250 −2.7 79.3 −0.84.1 Carbocolor Cancarb Thermal 8 250 −7.7 74.2 −1.1 4.9 CarbocolorCancarb Thermal 12 250 −12.2 69.7 −0.7 4.6 Carbocolor Cancarb Thermal 15250 −15.0 68.7 −0.8 4.3 Thermax Stainless Cancarb Thermal 5 250 −3.479.5 −1.2 3.9 Thermax Stainless Cancarb Thermal 10 250 −9.5 73.6 −1.04.4 Thermax Stainless Cancarb Thermal 15 250 −12.8 69.8 −1.5 5.1Sevacarb MT Sevalco Thermal 5 300 −2.0 80.9 −1.0 3.5 Sevacarb MT SevalcoThermal 8 300 −6.5 76.2 −1.0 3.6 Sevacarb MT Sevalco Thermal 15 300 −9.374.3 −1.2 4.5 Thermax Stainless Cancarb Thermal 5 250 0.7 82.2 −1.4 5.1Thermax Stainless Cancarb Thermal 10 250 −9.1 72.3 −1.2 5.1 ThermaxStainless Cancarb Thermal 15 250 −15.5 67.6 −1.1 2.6 SCD530 PureblackColumbian Thermal 5 250 −2.2 80.6 −0.9 4.2 SCD530 Pureblack ColumbianThermal 10 250 −4.4 77.4 −0.7 4.2 SCD530 Pureblack Columbian Thermal 15250 −8.8 73.7 −1.2 4.7 Sevacarb MT Sevalco Thermal 5 300 −2.6 80.4 −1.24.3 Sevacarb MT Sevalco Thermal 10 300 −6.6 75.1 −1.8 4.5 Sevacarb MTSevalco Thermal 15 300 −6.8 75.2 −1.0 3.9

FIG. 2 shows the reheat versus L* relationship for the samples ofExample 1. Faster reheat is represented by an increasing negative valuealong the x-axis. Increasing darkness of the polymer is represented by areducing L* value. The relationships for Furnace and Thermal carbonblacks are highly linear and quite distinct. The Thermal carbon blacks(line 30 in FIG. 2) show lighter polymer at any given level of reheatthan the Furnace carbon blacks (line 32 in FIG. 2). For example, at areheat of minus 10 seconds, a typical current manufacturing requirement,the difference in L* between Thermal and Furnace carbon blacks is about8 units. The Thermal carbon blacks gave superior L* performance in theresin.

FIG. 3 shows the reheat versus a* relationship for the samples ofExample 1. Increasing redness of the resin is represented by anincreasing positive value on the a* axis. All of the samples show asmall variation in a* within the range of 0 to minus 1.5 units. However,linear regression lines show a rising a* for the Furnace carbon blackswith faster reheat (line 42 in FIG. 3), but a flat trend with theThermal carbon blacks (line 40 in FIG. 3).

FIG. 4 shows the reheat versus b* relationship for the samples ofExample 1. Increasing yellowness of the resin is represented by anincreasing positive value on the b* axis. Again, although therelationships for the two forms are more scattered than for L*, the b*is always higher for the Furnace carbon blacks over the whole reheatrange. Therefore, the Thermal carbon blacks gave superior color on thebasis of the yellowness of the resin. The linear regression lines forthe two forms show an increasing trend with the Furnace carbon blacks(line 52 in FIG. 4), but a flat trend with the Thermal carbon blacks(line 40 in FIG. 4). Thus, at increasingly faster reheat, Thermal carbonblacks do not impair the color, whereas the Furnace carbon blacks leadto an increasingly yellow resin.

In considering FIGS. 3 and 4 it is well understood that a* and b* of thePET produced on a batch reactor is more subject to variation than L*. Atan otherwise fixed composition, L* is primarily a function of the typeand level of reheat agent used. However, a* and b* are influenced byreaction temperatures and other factors during melt polymerisation,solid state processing and injection molding that can lead todegradation of the resin. Further variation in a* and b* will also becaused by small differences in the levels of added toner and theirconcentrations retained in the final polymer.

In Example 1 only the relationship between reheat and color isconsidered. Plots of carbon black addition level against reheat, whichmight be subject to scatter due to inaccuracies in carbon black additionlevel or differences in the retention level of carbon black in the finalbottle, are not necessary to show this relationship.

The data from Example 1 can be seen as two separate groups distinguishedby the manufacturing route, and hence the mean particle diameter of thecarbon black. Thus, in terms of the two factors generally understood tobe the most important indicators of resin color, that is L* and b*,Thermal carbon blacks show an unexpected clear improvement over Furnacecarbon blacks at any level of reheat improvement.

Furnace carbon blacks with 100 nm particle size do not show superiorcolor to Furnace carbon blacks with 20 nm particle size. Hence theimprovement shown in Example 1 is only demonstrated at a particle sizeof at least 250 nm.

EXAMPLE 2 Polypropylene

PP compositions to demonstrate the present invention were prepared bycompounding different types of carbon black into RE420MO polypropylenemade by Borealis. 5 ml of liquid paraffin was added to 5 kg of the PPgranules in a bag blender that was then tumbled to coat the granuleswith a thin film of paraffin. The carbon black was added to the coatedgranules in an amount to give the desired concentration in the finalcomposition and the bag tumbled again to ensure an even adhesion ofcarbon black. The coated granules were then compounded through an APVMP2030 twin screw extruder, where the extrudate was quenched and re-cutinto granules. This intermediate material was compounded again through aBoston-Matthews single screw extruder fitted with a 4-section CavityTransfer mixer at the outlet. The extrudate was again quenched and cutinto granules to provide the final composition.

Plaques were moulded from these compositions on a Krupps KR35 extruderin the same way as described for PET in Example 1. Reheat and colormeasurements were made on these plaques using the methods describedabove. The data obtained for these samples are shown in Table 2, wherethe reheat is quoted as the final plaque temperature. As in Table 1 forPET, the carbon blacks used to make these compositions are groupedaccording to the primary particle diameter claimed by the manufacturer.

TABLE 2 PP plaque reheat and color data (Example 2) Mean particle Plaquefinal Addition diameter/nm temp./C. Plaque Plaque Plaque Carbon blackManufacturer Type level/ppm (manufacturer) (mean 3 tests) L* a* b* None— — — 62.1 78.8 −0.3 5.3 None — — — 61.8 79.4 0.1 3.3 None — — — 62.675.1 0.4 6.8 None — — — 62.5 76.0 0.1 7.3 Printex F alpha DegussaFurnace 1 20 64.9 72.2 0.4 5.0 Printex F alpha Degussa Furnace 2 20 64.573.1 0.5 6.3 Printex F alpha Degussa Furnace 5 20 67.5 65.2 1.7 8.1Printex F alpha Degussa Furnace 10 20 73.4 48.8 1.4 9.2 Printex F alphaDegussa Furnace 10 20 71.4 53.9 1.2 10.0 Printex F alpha Degussa Furnace10 20 71.1 53.6 2.4 9.6 Printex F alpha Degussa Furnace 15 20 74.3 45.62.8 10.2 Printex F alpha Degussa Furnace 20 20 77.2 38.0 3.0 10.0 Vulcan6 Cabot Furnace 5 24 67.6 64.6 0.9 8.7 Vulcan 6 Cabot Furnace 10 24 71.453.1 1.5 10.7 Vulcan 6 Cabot Furnace 10 24 71.4 53.2 2.6 10.4 Vulcan 6Cabot Furnace 20 24 77.0 37.3 3.3 10.9 Elftex 254 Cabot Furnace 10 2572.0 53.7 2.5 8.9 Special black # 4 Degussa Furnace 5 25 66.8 62.5 1.310.1 Special black # 4 Degussa Furnace 10 25 69.8 54.5 1.9 12.1 ThermaxStainless Cancarb Thermal 5 250 64.8 71.7 0.4 6.4 Thermax StainlessCancarb Thermal 10 250 67.3 68.4 0.4 6.2 Thermax Stainless CancarbThermal 25 250 72.6 59.5 0.3 5.6 Thermax Stainless Cancarb Thermal 50250 80.1 47.4 0.2 4.4 Sevacarb MT Sevalco Thermal 5 300 64.2 73.1 0.46.2 Sevacarb MT Sevalco Thermal 10 300 66.1 70.8 0.4 6.1 Sevacarb MTSevalco Thermal 25 300 70.3 64.6 0.5 6.0 Sevacarb MT Sevalco Thermal 50300 75.4 55.0 0.3 5.2

From the data in Table 2, FIGS. 5, 6 and 7 show the final plaquetemperature plotted against L*, a* and b*, respectively. The samerelationships between the reheat temperature and individual colorcomponents are shown in FIGS. 5 to 7 for Example 2 as were shown inFIGS. 2, 3 and 4 from Example 1. Again, the data show two distinctgroups according to the type of carbon black in the composition, withThermal carbon blacks showing higher L*, and lower a* and lower b* thanthe Furnace carbon blacks at any given level of reheat. Thermal carbonblacks therefore unexpectedly yield superior resin color in PP in thesame way as in PET.

EXAMPLE 3 Polypropylene Preform Blowing

To demonstrate the present invention in a typical bottle process, a PPpreform blowing experiment was performed using preforms moulded from twoof the compositions described above, one containing a Furnace carbonblack and the other containing a Thermal carbon black. In order toquantify the reheat advantage conferred by the different blacks theexperiment was set up to measure the reduction in the preform heat uptime possible whilst maintaining satisfactory blowing of the bottles.

The experiment was carried out using 23 g weight preforms from which 500ml volume bottles were blown. The preforms were injection moulded undertypical PP injection moulding conditions at a melt temperature of 220 Cand mould temperature of 15 C on a single cavity injection mouldmachine. A separate laboratory blowing machine made by SIPA andspecifically designed for the production of PP bottles, was then used toblow the bottles. The blowing machine had two infrared heating ovensseparated by an air gap to pre-heat the preforms to the temperaturerequired for blowing. Each oven had a maximum capacity of 10,000 wattsconsisting of 5×2000 watt infrared heaters arranged vertically to heatthe full length of the preform body. The preforms were spun verticallyon rotating holders throughout to ensure an even temperaturedistribution. In a continuous procedure the preforms were passed throughthe first oven over a period of about 60 to 80 s, through the air gapfor a further 60 to 80 s to allow the temperature to equilibrate, andthen through the second oven for a further 60 to 80 s. After another 10s equilibration in air, the heated preforms were finally delivered tothe blowing station.

To measure the cycle times, both ovens were fixed at 8900 watts to givea combined 17,800 watts output. The cycle time of the complete heatingand blowing process was then adjusted so that the time spent by thepreforms in the ovens gave a temperature that permitted the optimumbottle to be blown. Control of preform temperature to achieve the bestblowing performance is well understood by those skilled in the art. Ifthe preform temperature is too low, the preform cannot be completelyblown into the bottle mould. If the temperature is too high, thematerial distribution is poor leading to variable thickness of thebottle wall. In this way the time required to heat preforms containingthe carbon blacks was measured relative to that required for the controlPP with no carbon black added. The cycle time savings observed forcompositions containing various levels of a Furnace carbon black(Degussa Printex F alpha) and a Thermal carbon black (Cancarb ThermaxStainless) are shown in Table 3 and graphically in FIG. 8. These carbonblacks have mean particle sizes of 20 and 250 nm respectively.

TABLE 3 PP preform blowing cycle time reduction data (Example 3) Meanparticle Cycle time Addition diameter/nm reduction from Carbon blackManufacturer Type level/ppm (manufacturer) control/% Plaque L* Printex Falpha Degussa Furnace 5 20 24.0 65.2 Printex F alpha Degussa Furnace 1020 31.0 53.6 Printex F alpha Degussa Furnace 25 20 44.4 32.0 Printex Falpha Degussa Furnace 50 20 48.2 15.5 Thermax Stainless Cancarb Thermal5 250 16.6 71.7 Thermax Stainless Cancarb Thermal 10 250 26.7 68.4Thermax Stainless Cancarb Thermal 25 250 36.8 59.5 Thermax StainlessCancarb Thermal 50 250 44.1 47.4

FIG. 8 shows that both types of carbon black in the PP lead tosignificantly reduced cycle times. However, from the different gradientsof their respective plots (lines 90 and 92 in FIG. 8), a similar cycletime reduction is achieved at a higher resin L* by using the Thermalcarbon black (line 90 in FIG. 8). These plots are therefore similar inform to the L* versus plaque reheat relationships in both PP and PET.Hence this Example 3 reinforces the observations made in Examples 1 and2. Thermal carbon black unexpectedly leads to superior resin color atany specific level of improved reheat compared to Furnace carbon black,and this difference can be shown in a practical preform blowingsituation.

The invention has been illustrated by detailed description and examplesof the preferred embodiments. Various changes in form and detail will bewithin the skill of persons skilled in the art. Therefore, the inventionmust be measured by the claims and not by the description of theexamples or the preferred embodiments.

We claim:
 1. A preform made from a resin comprising polyethyleneterephthalate and from 2 to 50 ppm by weight of carbon black, based onthe weight of the resin composition including the carbon black, whereinthe carbon black has a mean particle diameter of at least 200 nm,wherein the carbon black is a carbon black that was made by a Thermalprocess.
 2. The preform of claim 1, wherein the carbon black has a meanparticle diameter in the range of 200 to 500 nm.
 3. The preform of claim2, wherein the carbon black has a mean particle diameter in the range of250 to 300 nm.